De Schutter, Geert

Marsavina, Liviu

Şoşdean, Corina

English

Ghent University Academic Bibliography

XIIIth Youth Symposium on Experimental Solid Mechanics, June 29th – July 2nd, Deˇcˇı´n, Czech RepublicINFLUENCE OF REAL CRACKS ON CHLORIDE DIFFUSIONC. Sosdean 1 , G. De Schutter 2 , L. Marsavina 3Summary: The novelty of this study consists in using drilled cores from a large scale OPCreinforced slab, exposed to a simulated accidental failure of the central support and subse-quent vertical loading until collapse, in order to determine the influence of real cracks inconcrete structures on the penetration of chlorides. The experimental results were obtainedwith the non-steady state migration test described in NT BUILD 492, using an electricalfield and real cracks. In order to study both the influence of rebars and cracks, refer-ence samples were used. The chloride penetration depth was measured with a colorimetricmethod on each specimen. From these penetration profiles the influence of cracks on thepenetration depth and the diffusion coefficient is investigated considering the crack pat-terns.Keywords: real cracks, chloride penetration, experimental results1 IntroductionChloride induced corrosion remains one of the major challenge; many studies were performed in the lastdecade in order to predict durability of concrete structures. In reality, these structures are frequently crackedeither by mechanical loading either they are a consequence of non-mechanical effects such as: temperatureand moisture gradients, expansive chemical reactions or are induced by corrosion of reinforcement in thepropagation stage of the chloride attack. Generally it is recognized that the existence of cracks acceleratesthe ingress of chloride ions. Thus, it is very important to have a better understanding of chloride diffusivityin cracked concrete.Several experimental studies were carried out in order to have a better image on this complex interactionbetween physical and chemical processes which is chloride ingress. Based on the crack preparation method,the reported experimental studies can be divided into two groups: destructive methods and non-destructivemethods. The former studies adopt different mechanical loading techniques to prepare cracks, such as wedgesplitting test [1, 2], three or four-point bending test [3], Brazillian splitting test [4, 5] and expansive coremethod [6]. Other studies use in order to simulate a crack by means of the positioning and removal of thincopper sheets before final setting of concrete [7, 8] or produce a crack by saw cutting concrete cylinderslongitudinally [9].Yet, none of these studies were made using samples obtained from real cracked structures.1Ing. Corina Sosdean, Politehnica University of Timisoara, Department Strength of Materials, Blvd. M. Viteazu, No. 1, Timisoara300222, Romania, email: corina.sosdean@yahoo.com2Dr.-Ing. Geert De Schutter, Ghent University, Magnel Laboratory for Concrete Research, Department of Structural Engineering,Technologiepark-Zwijnaarde 904, B-9052 Ghent, Belgium, email: Geert.DeSchutter@UGent.be3Dr.-Ing. Liviu Marsavina, Politehnica University of Timisoara, Department Strength of Materials, Blvd. M. Viteazu, no. 1,Timisoara 300222, Romania, email: msvina@mec.upt.ro116XIIIth Youth Symposium on Experimental Solid Mechanics, June 29th – July 2nd, Deˇcˇı´n, Czech Republic2 Experimental program2.1 Concrete samples and crack configurationThe samples used in this study were drilled from a cracked RC slab of 140mm thickness and 1800mmwide, having the total length of 14.30m. This slab was exposed to an artificial failure of the central supportand subsequent vertical loading until collapse. A detailed description of the test set-up and the results for theexperimental large-scale tests are described in [10, 11]. The 8 drilled cores used in this research have 100mmdiameter and 50mm thickness; the positioning of the rebars and of the cracks can be observed in Figure1; itcan be seen that the cracks go all the way through the samples; the average crack width of each sample wasmeasured before the non-steady state migration test using the optical microscope.Figure 1: Drilled samples with the positioning of cracks and rebars2.2 Testing methodOn these drilled cores a non-steady state migration test was performed according to NT BUILD 492 [12].Before testing, the samples were vacuum saturated with a saturated Ca(OH)2 solution. Afterwards an externalelectrical potential of 30 Volts was applied on the samples for 24 hours, forcing the chloride ions from the10% NaCl solution to migrate into the specimens (the exposed surface was the outer surface). After the test,the samples were cut in 5 parts each and sprayed with 0.01N AgNO3 solution and using the colorimetricmethod [13] the chloride penetration profile is determined.3 Results and discussions3.1 Penetration depthIn Figure 2 the mean penetration profile is presented for sample S4. On the vertical axis, the crack is repre-sented, in five different points, corresponding to the faces where the penetration depths were determined: A,B, C, D, and E. The results show an almost uniform distribution of the chlorides, even though the crack is notsituated in the middle of the sample. Also, it can be observed that the highest penetration depth is 27mm,even though the crack goes all the way through the sample.3.2 Migration coefficientFigure 3 shows the effect of crack width and rebar position on the diffusion coefficient. It can be easilyseen that the migration coefficient increases with the existence of cracks; when increasing the crack width117XIIIth Youth Symposium on Experimental Solid Mechanics, June 29th – July 2nd, Deˇcˇı´n, Czech RepublicFigure 2: Chloride penetration depth for sample S4 with the localization of the crackfrom 0 (reference sample) to 173.2µm (sample SA), the migration coefficient increases from 5.96x10−12to 10.40x10−12m2/s. As seen in Figure 1, samples S13 and SA have rebars on both directions and havethe highest diffusion coefficient: 11.09x10−12, respectively 10.40x10−12m2/s. Samples S25, SB and S7have the rebar perpendicular on the crack orientation, and the migration coefficients values are pretty close.Even though the crack width for sample S6 is 153.87µm, the value of the diffusion coefficient is pretty low:6.53x10−12m2/s; a possible explanation could be the positioning of the rebar which intersects the crack onlyclose to the edge. Further investigation needs to be carried on in order to have a better understanding of theinfluence of the rebar positioning on the diffusion process of cracked concrete.Figure 3: Comparison of diffusion coefficients according to crack width and rebar position4 ConclusionsThe following conclusions can be drawn from the present study:1. Even though the crack goes all the way through the sample, the chloride profile has a uniform pattern.2. It seems that the positioning of the rebars have an influence even bigger that the influence of crack118XIIIth Youth Symposium on Experimental Solid Mechanics, June 29th – July 2nd, Deˇcˇı´n, Czech Republicwidth, on chloride penetration, which requires further study in the future.5 AcknowledgmentThis work was done in the framework of Bilateral Scientific Agreement between Ghent University, Belgiumand Politehnica University of Timisoara, Romania. Also, the financial support by the Special Research Fund(BOF) of Ghent University is greatlfully acknowledged.References[1] Yoon, I.S. et al. Long/short term experimental study on chloride penetration in cracked concrete. KeyEngineering Materials, vol. 417-418, pp. 765-768 (2010).[2] Schlangen, E. et al. Measurement of chloride ingress in cracked concrete. In: Audenaert K., MarsavinaL., De Schutter G. (eds), International RILEM workshop on transport mechanisms in cracked concrete.Acco, Leuven pp 19-25, 2007.[3] Ye, H. et al. Influence of cracking on chloride diffusivity and moisture influential depth in concretesubjected to simulated environmental conditions. Construction and Building Materials, vol. 47, pp. 66-79 (2013).[4] Aldea, C.M. et al. Effect of cracking on water and chloride permeability of concrete. Journal of Materialsin Civil Engineering, ASCE, vol. 11(3), pp. 181-187 (1999).[5] Jang, S.Y. et al. Effect of crack width on chloride diffusion coefficients of concrete by steady-state mi-gration tests. Cement and Concrete Research, vol. 41(1), pp. 9-19 (2011).[6] Ismail, M. et al. Effect of crack opening on the local diffusion of chloride in inert materials. Cement andConcrete Research, vol. 34(4), pp. 711-716 (2004).[7] Marsavina, L. et al. Experimental and numerical determination of the chloride penetration in crackedconcrete. Construction and Building Materials, vol. 23(1), pp. 264-274 (2009).[8] Audenaert, K. et al. Influence of cracks on the service life of concrete structures in a marine environment.Key Engineering Materials, vol. 339, pp. 153-160 (2009).[9] Pour-Ghaz, M. et al. Numerical and experimental assessment of unsaturated fluid transport in saw-cut(Notched) concrete elements. ACI Special Publication SP266-06, vol. 266, pp. 73-86 (2009).[10] Caspeele, R. et al. Structural reliability of concrete slabs considering tensile membrane action. Safety,Reliability and Risk Analysis: Beyond the Horizon, Proceedings, pp. 2713-2720 (2013).[11] Gouverneur, D. et al. Experimental investigation of the load-displacement behavior under catenaryaction in a restrained reinforced concrete slab strip. Engineering Structures, vol. 49, pp.1007-1016(2013).[12] NT BUILD 492. Concrete, Mortar and Cement-Based Repair Materials: Chloride Migration Coefficientfrom Non-steady-state Migration Experiments. NORDTEST, 1999.[13] Otsuki, N. et al. Evaluation of AgNO3 solution spray method for measurement of chloride penetrationinto hardened cementations matrix materials. ACI Materials Journal, 89 (6), pp. 587-592 (1992)119

Influence of real cracks on chloride diffusion

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Influence of real cracks on chloride diffusion

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